JP2000208342A - Magnetic integration of planar inductors for switched power converters - Google Patents

Abstract

Kind Code: A1 Provided is a magnetic integration of a planar inductor (20) for a switched power converter that includes a filter means connected to a load to provide a zero ripple current. A planar inductor (20) includes a core having a standardized core section of an E-shape, the outer leg of which has a second magnetically coupled to obtain a leakage inductance (21-2). The first coil (21) and the second coil (22) are wound respectively. Thus, a common magnetic flux, each maintained by both coils (21) and (22), is conducted into the ferromagnetic circuit formed by the outer legs of the core and is associated with the leakage inductance (21-2). Magnetic flux is directed into one outer leg and the central leg.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetically integrated planar inductor used in an energy conversion process, wherein input and / or output filter means are used in a switched power supply converter. The present invention can be used in, but is not limited to, switched power converters, especially for low power and low voltage applications, and facilitates high levels of integration.

[0002]

BACKGROUND OF THE INVENTION A composite inductor including two or more coupled windings and used in a switched energy conversion process is disclosed in U.S. Pat. No. 5,481,238, which is incorporated herein by reference. Are known.

[0003] Output filters including composite inductors implemented by the aforementioned US patents are used in several converters, such as buck converters and boost converters.

[0004] The composite inductor proposed in that patent is:
A first inductor having a first winding on a first magnetic core;
A second inductor having a second core outside the winding coil of the first inductor, and a second winding around the first winding and the second core. One end of the first winding and a corresponding end of the second winding are electrically connected.

A major drawback of the inductors described in the above-mentioned US patents is that special cores of different sizes and magnetic materials are used to obtain the proper electrical characteristics of the output filter of the switched power converter. To
The cost is high because of the complexity of manufacturing.
Therefore, the manufacturing process is not fully automated.

[0006]

Therefore, there is a need to develop filter means, including induction means, having a manufacturing process in which fully automated and standardized elements are used.

As a result, the overall cost of the filter means is reduced, thereby reducing the overall cost of the switched power converter equipped with the filter means.

[0008]

SUMMARY OF THE INVENTION To overcome the above-mentioned problems, planar inductors used in some types of switched power converters having filter means for smoothing the current flowing in the power converter. We propose a magnetic integrated body. And planar inductors are the object of the present invention.

[0009] The configuration of the planar inductor of the present invention is such that the current supplied to the load satisfies the zero ripple condition, and furthermore, that the manufacturing process has a standardized element, for example, an E-shaped section, and special In order to use a planar magnetic core that does not require complicated machining, the construction process of the inductor is changed.

[0010] As a result, the reproducibility of the electrical properties of the planar inductor is guaranteed during the manufacturing process, so that the properties are not affected by the slight differences that can occur during said process. Thus, the cost of the planar inductor of the output filter is significantly reduced, and the overall cost of the converter is also reduced.

[0011] The switched power converter achieves a high overall efficiency of the process of converting the voltage received from the voltage source to the output voltage, and also responds quickly to changes in load, and therefore has a low profile and size. Can be used particularly in applications requiring low power and voltage.

[0012] The planar inductor includes a core having a standardized core section of E-shape, the outer legs of which include:
A first coil and a second coil, each magnetically coupled to each other so as to create a large leakage inductance, are wound respectively, so that one end of the first coil and the corresponding end of the second coil Are electrically connected at a second node. As a result, the common magnetic flux respectively maintained by both coils is conducted into the ferromagnetic circuit formed by the outer legs of the core, and the magnetic flux associated with the leakage inductance is reduced by one outer leg and the center. It will be guided by the legs.

A more detailed description of the invention will be made in the following description with reference to the accompanying drawings.

[0014]

FIG. 1 shows a single output buck converter incorporating filter means 14 connected directly to a load. The means is configured to zero the ripple (zero ripple condition) and smooth the output current.

The buck converter is merely used as an example to better explain the present invention, and has all output or input filters, and other types of switched to achieve the same result. It is possible to use converters.

The step-down converter is connected to a voltage source via input terminals 11 and 12. One of the input terminals 12
Represents a common voltage reference for the converters.

One of the input terminals 11 is connected to a first switching means 13, for example, a field effect transistor or a MOSF.
It is connected to the ET type first terminal 13-1. The second terminal 13-2 is connected to the input terminal 14-1 of the filter unit 14. The first switching means includes an output terminal 14-
And a third terminal (not shown) from which a signal is received to adjust the on and off periods of the first switching means 13 to produce an adjusted output voltage across 3 and 14-4. .

The first node 16 located on the conductor connecting the second terminal 13-2 to the input terminal 14-1 is connected to the first terminal 15-1 of the second switching means 15. , The second terminal 15-of the second switching means 15.
2 is connected to the common voltage reference of the converter and forms a rectifier branch. For example, the second switching means 1
5 is a unidirectional conduction device such as a diode.

The terminal 14-2 of the filter means 14 is also connected to a common voltage reference. The filter means 14 receives energy from the voltage source during the on-period of the first switching means 13 and outputs a smoothed output voltage across the output terminals 14-3 and 14-4 and the output of the ripple near zero. Generates current. This voltage and current are respectively applied to the load. This load may be a communication device.

The filter means 14 includes a planar inductor 20 including at least one first coil 21 located on a conductor connecting the terminal 14-1 to the terminal 14-3, and a second coil 22. And the second storage capacitor 2
2-1 is connected in series with the terminal 14-1 and the first coil 21.
Connected to a second node 24 located between the ends of.
Therefore, this series connection is connected in parallel with the second switching means 15.

The first storage capacitor 21-1 is connected in parallel with the load for smoothing the current flowing through the first coil 21, so that the average value of the current is zero.

The two coils 21 and 22 of the inductor 20 are wound around a magnetic core 23 and are magnetically coupled to each other. The coupling coefficient between the coils 21 and 22 is less than 1 because these coils have different numbers of turns.

The inductor 20 is configured to introduce a large leakage inductance between the coils 21 and 22. The leakage inductance is represented in FIG. 1 by a third coil 21-2, which is connected in series with the end of the first coil 21 and the end of the first capacitor 21-1.

Since the current ripple is a function of the ratio of the magnitude of the voltage drop across the third coil 21-2 to the value of its inductance to meet the zero ripple condition of the output current, the third coil The magnitude of the inductance of 21-2 must reach a high value. Therefore, the value of this inductance must be as high as possible.

The voltage seen at the inductance 21-2 is the voltage difference between the voltage of the second capacitor 22-1 and the voltage of the first capacitor 21-1.

FIG. 3 shows a preferred embodiment of a magnetic core 23 used in the construction of the inductor 20 to achieve the desired result in the present invention. The core 23 includes at least two standardized core sections, at least one of which is an E-shape or tripod core.

FIG. 2 shows each coil 21 and 22 respectively wound around the outer leg of the E-section, one end of the first coil 21 and the corresponding end of the second coil 22. The units are electrically connected at a second node 24.

To simplify the manufacturing process of the inductor 20, the turns of each coil 21 and 22 are placed on a printed circuit board and may be multilayer. Thus, the manufacturing process of the planar inductor 20 of the present invention is relatively insensitive to tolerances, ensuring a high degree of reproducibility of the process.

The operation of the step-down converter is described as follows. During the period in which the first switching means 13 is conducting, the same power as that applied across the input terminals 11 and 12 is applied to the input terminal 14-of the filter means 14.
1 and 14-2. These powers are greater than the voltage present across output terminals 14-3 and 14-4.

As a result, capacitors 21-1 and 22
An increasing current flows from terminals 11 and 12, which charge -1. Inductor 20 begins to charge, stores a certain amount of energy, and supplies current to the load. During this time interval, a direct transfer of power from the input to the output occurs.

At the moment when the first switching means 13 is turned off, the current flowing into the filter means 14 cannot be suddenly cut off. Therefore, the second switching means 15 starts conducting.

At this instant, the voltage applied to the input of filter means 14 is lower than the voltage applied to terminals 14-3 and 14-4. Thus, the current flowing through the filter means 14 is in the same direction as before, but is decreasing.
At the moment when the first switching means 13 resumes conduction,
The second switching means 15 stops conducting and the cycle starts again.

The primary purpose of the magnetic integration of the planar inductor 20 is to divert alternating current (AC) received by the filter means 14 to the second coil 22. Therefore, the first coil 21 has a direct current (D
C) only, whereby the output voltage is more easily smoothed. As a result, the series combination of the second coil 22 and the second capacitor 22-1 receives only the AC current whose average value is equal to zero. Therefore, the output current satisfies the zero ripple condition.

The electrical characteristics of the filter means 14 are not changed by incorporating the series coupling described above. Thus, the inductor 20 is configured to confine the common magnetic flux maintained by the two coils 21 and 22, respectively, in a ferromagnetic circuit formed by the outer legs of the magnetic core 23. Then, the magnetic flux maintained by the third coil 21-2 is guided into a ferromagnetic circuit formed by the central leg and the outer leg around which the first coil 21 is wound. The center leg has a predetermined air gap 23-1 to limit the magnitude of this magnetic flux.

Similarly, the outer legs are provided with a first air gap 23 in the central leg to limit the magnitude of the common magnetic flux.
It has a second air gap much smaller than -1 to prevent the magnetic core 23 from saturating.

FIG. 4 shows the filter means 14 of the present invention in a boosted switched power converter. The operation is the same as the operation of the step-down converter, and will not be described here.

From the above description, it can be seen that the filter means 1 of the present invention is used.
The switched power converter comprising 4 is preferably implemented with an integrated planar magnetic device, the coils of which are placed on a printed circuit board and arise during a manufacturing process which can be automated by the use of standardized elements. It can be inferred that it shows little sensitivity to changes. Such converters are compact in size, have low profiles, and require both low power and low voltage, ie, are particularly useful in applications that supply power to end loads.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a step-down converter according to the present invention.

FIG. 2 is a front view of an inductor core used in the configuration of the step-down converter, showing a magnetic flux distribution according to the present invention.

FIG. 3 is a diagram showing a preferred embodiment of an inductor core used in the configuration of the step-down converter according to the present invention.

FIG. 4 is another circuit diagram of the boost converter according to the present invention.

[Explanation of symbols]

 11, 12, 14-1, 14-2 Input terminal 16 First node 13 First switching means 13-1, 15-1 First terminal 13-2, 15-2 Second terminal 14 Filter means 14 -3, 14-4 Output terminal 15 Second switching means 20 Planar inductor 21 First coil 21-1 First capacitor 21-2 Leakage inductance 22 Second coil 22-1 Second capacitor 23 Magnetic core 23- 1, 23-2 air gap 24 second node

Claims (5)

[Claims] 1. A magnetic integration of a planar inductor (20) for a switched power converter including filter means (14) directly connected to a load for supplying a current having zero ripple to the load, said magnetic inductor comprising: The planar inductor (20) has at least one of the E-type standardized magnetic cores.
A magnetic core (23) formed by two sections and a first coil (21) and a second coil (22) magnetically coupled to each other to obtain a leakage inductance (21-2); One end of a first coil (21) and a corresponding end of the second coil (22) are electrically connected at a common second node (24), and the first coil ( 21) and each of the second coils (22) are respectively wound around first and second outer legs of the standardized core section, the first coils (21) and the A planar inductor (20) for directing a common magnetic flux, each maintained by both of said second coils (22), into a ferromagnetic circuit formed by said outer legs of said core (23). of Care integration body. 2. The method according to claim 1, wherein the first coil (21) is connected to the second
The magnetic integrated body of the planar inductor (20) according to claim 1, wherein the number of turns of the coil (22) is different from that of the coil (22). 3. A ferromagnetic circuit in which a magnetic flux maintained by the leakage inductance (21-2) is formed by a central leg and an outer leg around which the first coil (21) is wound. The magnetic integrated body of a planar inductor (20) according to claim 1 or 2, characterized in that: 4. The size of the leakage inductance (21-2) is limited by a predetermined first air gap (23-1) located at a central leg of the magnetic core (23). The planar inductor (2) according to claim 3,
0) Magnetic integrated body. 5. The magnetic flux maintained by the first coil (21) and the second coil (22), respectively, is equal to the magnitude of the second magnetic flux located at the outer leg of the magnetic core (23). The value of the second air gap is limited by the air gap and the value of the first air gap (23−
2. A value smaller than the value of 1).
A magnetic integrated body of the planar inductor (20) according to the above.